This is a study of cell plasma membrane structure and functions, employing cell-vesicle interactions to probe intermembrane lipid and protein transfer and the selective translocation and sequestration of phospholipids. Energy dependent translocation of aminophospholipds has been demonstrated in human erythrocytes and platelets. The molecular properties of mechanism will be studied in intact erythrocytes and in red cell membrane preparations of progressive simplicity. Evidence for selective lipid translocation and sequestration will be sought in other cell types, including normal and transformed mammalian lymphocytes. Cell-to-vesicle protein transfer will be examined as a means of generating intact model membranes containing lymphocyte surface determinants bound in native orientation; such protein-vesicle complexes will be useful in studies of intercell recognition and fusion. Similarly, protein transfer from encapsulated mammalian viruses will be studied, with the goal of preparing liposomes targeted to cells vulnerable to viral invasion.